Author Topic: K-fab pilot heads  (Read 1764 times)

PilotHawK

  • Hero Member
  • *****
  • Posts: 616
  • Karma: 0
    • View Profile
K-fab pilot heads
« on: April 19, 2004, 10:10:47 PM »
I accomplished one of my major goals of the weekend and had a hell of a time doing it too!

I met up with Redrider, Rocketman, Luke, Vroom, and a couple of Redrider's friends at Durham Plantaion Friday night. First let me say that this place is an awesome place to ride. Nice trails, nice facilities, and one hell of a chef!

I arrived late Friday night after working my butt of all day and wondering if I would even have a pilot to ride. To make a long story short, My machinist fell through on getting a cylindere bored for me so I had to go to my backup guy. He did a bang up job on the cylinder and really helped me out when I was in a bind (and I couldn't beat the price, $35 bucks).

I had been trying to make rough calculations all week for the new head, and cylinder combination, and potential problems I might run in to during the testing of the head. I had to guess at a lot of numbers because I didn't have the cyinder available for most of my measure ments and was using a lot of data I couldn't actually verify.

What I did is a major NO NO in the pilot world. I drove 5 hours with a non-running pilot, a box of parts and a lot of hopes. I knew what I was doing, but how many times do things actually work out as anticipated? This was one of the times that things worked out perfect!

With the use of an enclosed trailer as a workshop (no dirt in my motor) Redrider and I proceeded to put a top-end on a pilot. I had already prepped the cylinder, head, and piston, had all the gaskets, and most of the necessary tools ready to go. After getting the cylinder on and realizing the exhaust port goes toward's the front, the Installation went as well as can be expected. No lost circlips, no missing  parts everything went smooth. (***Since I could not pressure test this motor after the top-end went on I used a very thin layer of yamabond on both sides of the base  gasket, and intake manifold gasket surfaces to ensure a leak free installation.) I decided to go with the torque specs for the stock head of 20 ft/lbs since this is such a stout unit.

Now for the whole purpose of this whole rebuild. I was declared a "test rat" for the new K-fab head and wanted to get good numbers so started with a fresh top-end to get numbers as good as I could. The head itself is a really BEEFY unit. The fit was great, and it looks like a real work of art. I was sent 2 domes and I measured the volume of each dome. The dome I chose to go with was the "low compression dome" and it had a volume of 48.9 cc (The "high compression dome" had a volume of 44.6 cc) I don't want to run race gas so no need for me to try the high compression dome (I will install it this weekend to check comprression for reference only).

Right after the rebuild and prior to starting the motor, the compression on 3 different compression guages was 152 (+/- 2)psi. Not bad considering the rings very little oil on them and were definately not seated.

This next part you can take however you want. There are 2 basic schools of thought on top-end break in proceedures. For this rebuild I went more with the put it together and run it school. I did do a 5 minute warm up right after we got the motor back together and to check for leaks or other problems. After that though, I flogged the pilot pretty good. After the initial warm up the compression came up to 162 psi (at this point I'm thinking cool!) After everything was back together the pilot fired right up like I had hoped it would, with the only issue being that it wouldn't idle. An adjustment to the idle screw fixed that (thanks Rocketman), and the pilot sounded great.

Now the first ride of the day. I topped off the tank with FRESH 93 octane fuel mixed at 40:1 (maxima super M). We headed out for the trails. I did take it fairly easy with the initial warmup and trail ride to make sure I had the motor up to operating temps (wiseco pistons do expand a little more than stock pistons). The first time out we rode 14 miles or so. I had no problems keeping up with the group, and the pilt ran great! It had been over a year since I had trail ridden this hard, and damn it was FUN! The motor was crisp and responsive, and the new found power was awesome.

When we got back to camp, I needed to check the jetting and compression. The plug (a new one) had already developed real good color (light pancake) at the base of the insulator, and the tip was dry with very little carbon on it. The compression was was impressed me the most. Now it was up to 172-174 depending on the guage! Keep in mind that I was running pump gas, and never noticed any sign of detonation. I will take the head of later this week, and look at the piston wash and possible signs of problems.

With all this said here is what I started with. A 2nd over stock piston in a stock cylinder. The piston to cylinder clearance was about 3x too much, and the ring end gap was 2x too large. The compression when warm was 140 psi. The stock head had a volume of 59 cc. What I have now is a Macdizzy ported cylinder at .040" over K-fab head at 48.9 cc. Stock head gasket, and both upper and lower ring end gaps set at .018". Now the compression is between 172 and 174 psi, and the thing rips!

I will post more data and pics later in the week or over the weekend as I take the head back off and try the "high compression" dome.

ludedude

  • Hero Member
  • *****
  • Posts: 1478
  • Karma: 0
    • View Profile
K-fab pilot heads
« Reply #1 on: May 05, 2004, 07:06:55 PM »
Just got mine yesterday

PH (or Moskito, but I figure you're out racing??), what were the markings on your domes?

I have:

1. stamped 49cc, R875...and then R .875 in red and 1.072 in blue
2. stamped R1, R1.000 in red, and 1.075 in blue
3. stamped R1125, 1.094 in blue

I'm guessing my 49cc is the same as the one you measure at 48.9...How did you perform the CC test...I like to do mine as well, and like to do it as close to the same as you did for comparison sake.

Wow, you gained 20psi on breakin/ring seating! I've never had that much gain  :shock:

0.040" over is that first or 2nd oversize?  :oops:

I will be testing the heads on 3 cylinders:
1. stock 1st oversize
2. MacDizzy, 1st oversize
3. ATVR 82mm

YeeHaa, can't wait....  :D  Have you done anymore measurements? Checked the dome again for detonation signs? 172 and no detonation...COOL! :o

Moskito

  • Sr. Member
  • ****
  • Posts: 396
  • Karma: 0
    • View Profile
    • http://www.yellowdogracing.com
K-fab pilot heads
« Reply #2 on: May 06, 2004, 09:55:10 PM »
Quote from: "ludedude"
Just got mine yesterday

PH (or Moskito, but I figure you're out racing??), what were the markings on your domes?

I have:

1. stamped 49cc, R875...and then R .875 in red and 1.072 in blue
2. stamped R1, R1.000 in red, and 1.075 in blue
3. stamped R1125, 1.094 in blue


Just use the "R" numbers.  The other numbers were ref numbers for machining.

R1125 will be highest comp number, R1 will be medium, R.875 will be low.

We won't talk about racing (I didn't finish last, but I didn't finish), but everything else in Mexico was a blast.
Moskito - Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming \'WOW-What a Ride!\'

dhjunkie

  • Full Member
  • ***
  • Posts: 161
  • Karma: 0
    • View Profile
K-fab pilot heads
« Reply #3 on: May 06, 2004, 10:20:52 PM »
Why do I see a big A$$ smile behind that monitor?????

ludedude

  • Hero Member
  • *****
  • Posts: 1478
  • Karma: 0
    • View Profile
K-fab pilot heads
« Reply #4 on: May 06, 2004, 10:54:17 PM »
Quote from: "Moskito"
Just use the "R" numbers.  The other numbers were ref numbers for machining.

R1125 will be highest comp number, R1 will be medium, R.875 will be low.


OK cool. Hope to do some testing this weekend  :D

Quote from: "Moskito"
We won't talk about racing (I didn't finish last, but I didn't finish), but everything else in Mexico was a blast.


Is that supposed to be "I didn't finish last, but I did finish)??

Glad you had a blast  :wink:

Moskito

  • Sr. Member
  • ****
  • Posts: 396
  • Karma: 0
    • View Profile
    • http://www.yellowdogracing.com
K-fab pilot heads
« Reply #5 on: May 07, 2004, 10:09:27 PM »
Quote from: "ludedude"
Is that supposed to be "I didn't finish last, but I did finish)??


Uhm....
Nope.  Didn't finish.  In fact, I was about 130 miles short.  But I wasn't last!
I hear only 30% of the vehicles finished.
But Man oh man Mexico was fun. 8)
Moskito - Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming \'WOW-What a Ride!\'

ludedude

  • Hero Member
  • *****
  • Posts: 1478
  • Karma: 0
    • View Profile
My data so far
« Reply #6 on: May 10, 2004, 11:18:36 AM »
Here's what I have so far....having the flu and one child with it too is slowing me down gettingto this...sorry

cylinder /dome-----current--------R0.875-----R1.000------R1.125
Stock-----------------???------------???----------???------------???
MacDizzy-------------???------------???----------???------------???   
ATVR-----------------135------------160---------160------------???

cylinder----bore (mm)   ----head cc      
Stock-------80.5-------   ----??      
MacDizzy---80.5-----------??      
ATVR-------82--------------??      

dome-------head cc         
R0.875------49cc
R1.000------??
R1.125------??